You sure have put yourself in a non risky position where we're either okay and you can complain here, or where we're good and you can celebrate your team winning.
If we pay the guy 18 Mil, he should play like QB14, and we should win 8 games and be the 14th best team in the league. So don't complain if that happens. And if its better then that and win 9 and make the playoffs, don't complain and say 'well he exceeded what he should have done but it's not good enough, we lost the playoffs so we should have tried a 3rd round qb instead'.
If Sam is paid like the 14th best QB in the NFL, if he exceeds that and we exceed the 14th best record will you be able to admit that it was a good signing and you're happy with it? Or are you going to play the "I told you so" game until we make a deep playoff run or win a SB.